In the grinding of cemented carbide tools and high hardness steels it is desirable to make available grinding tools which can be used without a liquid lubricant or coolant since operators in most instances would prefer to grind dry thus avoiding the inconvenience and expense of providing a coolant source. Furthermore, the use of a coolant interferes with the observation, by the operator, of the grinding process.
The failure of ceramic bonded wheels to compete in this area is due to a severe loading which occurs on grinding. This, in turn, leads to high power loads, heating, and wheel breakdown or even breakage.
Grinding wheels employing ceramic bonds have recently been introduced which contain 40% or more carbon, a portion of which is graphite. These wheels have an open porosity 15% or more and are impregnated with a lubricant such as stearic acid which liquifies on the wheel surface during grinding. Such wheels have been found inadequate for grinding cemented carbides at conventional grinding rates for carbide grinding with diamond wheels.
This invention also relates to self-sharpening hones. Under desirable operating conditions for honing carbide most standard diamond hones do not perform in an optimum manner. Whether they are metal-, resinoid-, or vitrified-bonded, the standard product will cut freely for but a short while (after dressing) and then progressively exhibit a lower and lower rate of cut to the point where additional dressing is necessary in order to maintain an economical honing operation. Due to the high cost of labor, it is very desirable to maintain a high rate of cut (high rate of carbide removal) and reduce dressing to a minimum or even eliminate, if possible.
We have found that by introducing an "inert" second phase into a vitrified-bonded diamond hone, we can change the breakdown behavior of the bond so that a self-sharpening action is obtained; leading to constant high rates of carbide removal with little or no "dressing" in the normal sense being required.
The present invention provides a ceramic bonded grinding tool, having graphite included therein, which equals or significantly out-performs the presently commercially available wheels for the dry grinding of carbides. When the wheel includes cubic boron nitride abrasive particles it is equal to or better than commercially available grinding wheels in grinding efficiency and superior in its low power requirements, for the grinding of high hardness steels.